Electro-pneumatic process controller



Aug. 6, 1968 K. 5. KREUTER 26,431

ELECTRO'PNEUMATIC PROCESS CONTROLLER 2 Sheets-Sheet 1 Original Filed May24, 1963 INVENTOR. Kenneth G. Kreuter ATTORNEYS Aug. 6, 1968 K. G.KREUTER ELECTRO-PNEUMATIC PROCESS CONTROLLER 2 Sheets-Sheet 2 OriginalFiled May 24, 1965 INVENTOR Kenneth G. Kreuier ATTORNEYS United StatesPatent 26,431 ELECTRO-PNEUMATIC PROCESS CONTROLLER Kenneth G. Kreuter,Goshen, ]nd., assignor to Robertshaw Controls Company, Richmond, Va., acorporation of Delaware Original No. 3,216,331, dated Nov. 9, 1965, Ser.No. 282,936, May 24, 1963. Application for reissue Dec. 9, 1966, Ser.No. 607,347

11 Claims. (Cl. 91-374) Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

This invention relates generally to process controllers utilizingelectro-pneumatic converters and more particularly, means for convertingan electric control signal, such as for example, a duration modulatedbinary electric signal, derived from a digital computer or other source,into a pneumatic control signal which ultimately positions,pneumatically, a control means such as the valve stem of a processcontrol valve.

In dynamic control systems such as process controls having integralcomputer means as the brain or monitor thereof, it is often necessary toconvert electric output signals from the computer into a functionallyrelated class of signals such as pressure and/or displacement.

It is an object of this invention to provide a process control system orthe like for first performing an electropneumatic conversion andsubsequently converting the resulting pneumatic signal into adisplacement functionally related to both the electric and the pneumaticsignals in the system.

It is another object of this invention to provide a process controlsystem or the like, wherein .[a duration-modulated binary electricoutput] on electric control signal from a digital computer or the likeis first applied to an electric motor means, and converted to an outputdisplacement of said motor means, then the motor displacement isconverted to a control pressure and that control pressure issubsequently converted to a final displacement, the final displacementbeing imposed on a movable control means.

Still another object of this invention is to provide a process controlsystem or the like, wherein [a durationmodulated binary electric output]an electric control signal from a digital computer or the like is firstapplied to an electric motor means, and converted to an outputdisplacement of said motor means, then the motor displacement isconverted to a control pressure and that control pressure issubsequently converted to a final displacement, the final displacementbeing imposed on a moval control means, said system including a novelintercoupled input drive and displacement feedback means, eflecting aposition balance whereby said system is highly stable.

Yet another object of this invention is to provide a position-balancedsystem for pneumatically positioning a control valve or otherdisplaceable control means in response to an electric control signalsuch as, for example, a duration-modulated multiple-state electricsignal.

Yet another object of this invention is to provide a new and novelposition-balanced transducer means for converting electric controlsignals to an output displacement.

These and other objects of the invention will become more [full] fullyapparent with reference to the following specification and drawingswhich relate to several preferred embodiments of the invention.

In the drawings:

FIGURE 1 is schematic of one embodiment of the system of the presentinvention with the novel structural components thereof shown[isometrically] in perspective;

Reissued Aug. 6, 1968 FIGURE 2 is a schematic of another embodiment ofthe system of the present invention with the novel structural componentsthereof shown [isometrically] in perspective; and

FIGURE 3 is a schematic pneumatic flow diagram illustrating anotherembodiment of the invention applicable to either of the system ofFIGURES l and 2.

Referring in detail to the drawings, and more particularly to FIGURE 1,the embodiment of the invention shown therein will now be described.

The electric input source 10 comprises first and second relay switches12 and 14, respectively, representative of the two different states of abinary signal. The coils of the relay switches 12 and 14 are selectivelyenergized by the binary output signal of a digital computer 16,generally shown in block diagram form as having two output leads "1 and"0" representing the binary output states of the said computer 16. Thecomputer senses variations in the parameters of a process or the likewhich is being controlled by the present invention.

The relay switches 12 and 14 are connected with a common terminal 18, towhich is connected a first power lead P A second power line Prepresenting the other side of a suitable power supply 20, is directlyconnected to the common or neutral input terminal 22 of a reversibleelectric [servo] motor 24.

The first relay switch 12 is connected to respond to a zero state outputfrom the computer terminal 0 and is provided with a terminal contact 26connected, via a lead 28, to an input terminal 30 on the [servo] motor24 which, when energized, causes the said motor to rotate in acounter-clockwise direction.

The second relay switch 14 is connected to respond to a unit stateoutput from the computer terminal I and is provided with a contactterminal 32 connected, via a lead 34, to an input terminal 36 on the[servo] motor 24 which, when energized, causes the said motor to rotatein a clockwise direction.

The [servo] motor 24 comprises the motive means of an electric-pneumatictransducer generally indicated by the numeral 38.

The transducer 38 further includes the rotary output shaft 40 of the[servo] motor 24, a manual override disk or wheel 42, integrally andcoaxially mounted on the shaft 40, a cylindrical hub 44 integral withthe wheel 42 and extending outwardly and coaxially therefrom, and aninput or control cam 46 integrally mounted on the outer end of the hub44 and adapted, along with the wheel 42 and hub 44 to rotate with and onthe axis of the motor shaft 40. The above-defined combination ofelements provides a mechanical displacement input to theelectropneumatic transducer 38 as a function of the electric signalinput to the [servo] motor 24 as will be hereinafter more fullydescribed.

A control follower 48 is provided for the control cam 46 in the form ofa bifurcated elongated lever pivoted at its unitary end St) to asuitable fixed pivot means 52. One leg of the bifurcated portion of thecontrol follower 48 is engaged with the periphery 54 of the control cam46, the said periphery 54 comprising the cam contour of the said controlcam. An adjustable cam indexing means is provided in the form of athreaded cam indexing detent 56 which screws in and output of a fixedmount 58 positioned by any suitable means adjacent the periphery 54 ofthe control cam 46. The indexing detent 56 is adapted to engage the fallsurface 60 on the peripheral cam contour 54 of the said control cam 46.

A leakport nozzle 62 having a leakport 64 in the tip thereof is mountedon the outer tip of an integral laterally extending arm 66 on athrottling range slide means 68 adjustably and slidably mounted forlongitudinal adjustment on the bifurcated portion of the controlfollower 48, via a throttling range set-screw 70.

The leakport nozzle 62 is supplied with pneumatic pressure by means of apressure hose 72 communicating with the pilot or signal chamber 74 of astacked multiple diaphragm type pneumatic relay 76. The pilot pressurein the pilot chamber 74 is derived from the main air supply chamber 78of the relay 76 via a bleed port 80 having an in-line flow restrictor 82therein.

The main air chamber 78 is supplied by a suitable pressure source 84 andis connected with the output chamber 86 of the relay 76, known in theart as either the branch or control pressure chamber, by the lower halfof a two-way relay poppet 88 seating internally of the main air chamber78.

The upper end of the poppet 88 seats within the output chamber 86 on adiaphragm carried floating valve seat 90, whereby the output chamber 86is controllably interconnected with the exhaust chamber 92. The valveseat 90 is part of a spacer structure 94 which separates and remainsmobile with the two diaphragms 96 and 98 which, combined with theinternal cavity of the relay 76, define the pilot, output and exhaustchambers 74, 86 and 92, respectively.

The exhaust chamber 92 is connected with the atmosphere via a vent port100. The branch pressure or output chamber is delivered to any device tobe controlled thereby via an output port 102.

The output port 102 is connected to the topwork of a pneumaticallypositioned valve, as will be hereinafter more fully described withrespect to FIGURE 3, the valve not being shown in FIGURE 1.

The valve stem 104 is displaceable in response to various values ofbranch pressure from the relay 76, and this displacement is utilized asthe input signal for the feedback mechanism 106 of the electro-pneumatictransducer 38.

An integral lateral extension 108, shown here as a flat radial lever, isprovided on the valve stem 104. One end of a flexible link such as aball chain or cable 110 is affixed to the extension 108, the other endand several convolutions thereof being wound on a rotatably mountedstorage drum 112. Thus, the drum 112 is adapted to be rotated by thechain 110 in response to a displacement of the valve stem 104.

The drum 112 is integrally and coaxially mounted for rotation with arotary shaft 114 which in turn drives an integrally and concentricallymounted first pinion gear means 116. The first gear 116 is intermeshedwith and adapted to drive a second pinion gear means 118, the saidsecond gear means being integrally and concentrically mounted on one endof a shaft 120.

A feedback cam means 122 is integrally mounted on the other end of theshaft 120 and is adapted to rotate therewith. The feedback cam contourcomprises the periphery 124 of the feedback cam and includes a fast fallsurface 126.

The cam shaft 120, the feedback cam 122, the control cam 46 and the[servo-] motor shaft 40 are mutually coaxial. The opposed end faces ofthe control and feedback earns 46 and 122, respectively, areinterconnected by way of torsion spring means 128 anchored at each ofits ends to one of the said end faces and coaxially disposed withrespect to the said cams.

Mounted immediately adjacent the periphery 124 of the feedback cam 122is an elongated feedback or leakport lever 130, pivoted at one end to apivot means 132, coaxial with the pivot means 52 of the controlfollower, and extending to a position whereby the surface of the saidleakport lever is engageable with the leakport 64 at a point adjacentthe other end thereof.

A vertically adjustable threaded detent 134 extends through the leakportlever 130 into engagement with the periphery 124 of the feedback cam 122and thus, comprises an adjustable cam follower for varying the verticalposition of the leakport lever 130 as a function of the angular positionof the feedback cam 122, and hence, the position of the valve stem 104.

A zero stop for the feedback cam 122 in the form of a fixed detent 136is positioned adjacent the periphery 124 of the said cam and is adaptedto engage the fast fall surface 126 when the cam is in the predeterminedzero position.

Referring now to FIGURE 2, a second embodiment of the invention will nowbe described, like parts to FIG- URE 1 bear the same numerals.

The electro-pneumatic transducer generally indicated at 138 is shown asincluding a first input pinion 140 is concentrically and integrallymounted on the [servo-] motor shaft 40. The first input pinion 140 isintermeshed with and adapted to drive a second input pinion 142, thesaid second pinion being an integral offset concentric portion of arotary leakport positioning disc assembly 144. The assembly 144 alsoserves as a manual override device.

An integral shelf 146 is provided adjacent the periphery of the diskassembly 144 and on that face of the said disk assembly 144 removed fromthe second input pinion 142. The shelf 146 is adapted to threadablyreceive a throttling range screw 148 therein which acts as a positioningand hold-down means for one end of a flat control lever 150 extendingoutwardly from the shelf 146 in a plane perpendicular to the face of thedisk assembly 144.

A leakport nozzle 152 is mounted through the control lever 150 adjacentthe free end thereof with the leakport 154 therein opening upward asshown. The leakport nozzle 152 is supplied with pressure from the relay76, already described with reference to FIGURE 1, via a pressure line ortube 156.

The feedback mechanism 158 of the embodiment of FIGURE 2 is identical tothat of FIGURE 1 as to the valve stem 104, integral extension 108, chain110, drum 112, drum shaft 114, first feedback pinion 116, secondfeedback pinion 118 and the rotary shaft 120.

The end of the shaft 120 removed from the second feedback pinion 118mounts an integral concentric leakport lever control disc assembly 160.The control disc assembly 160 includes a longitudinally extending stoppin 162 which is radially offset with respect to the axis of rotation ofthe rotary shaft 120 and control disk assembly 160.

The control disk assembly 160 and the positioning disk assembly 144 arecoaxially disposed. The opposing faces of the said disc assemblies areresiliently coupled together by first and second axially disposedtorsion springs 164 and 166, respectively, the said springs being spacedapart at their respectively adjacent end portions by an axially disposedspacer means 168. The other end of the first torsion spring 164 issuitably anchored to the face of the positioning disk assembly 144 andthe other end of the second torsion spring 166 is suitably anchored tothe face of the control disc assembly 160.

As shown, the spacer 168 is of a cylindrical shape and in combinationwith the torsion springs 164 and 166 comprises a biased pivotal mountingfor the leakport lever 170, which extends radially outward from thespacer 168 to a position above and adjacent the leakport 154.

Referring now to FIGURE 3, the flow diagram into and out of the relay76, excluding the leakport connections thereto, is shown with a manualcontrol valve 172 which is adapted to selectively bypass the relay 76and connect the main air supply 84 directly with the valve top work 174via a pressure line 176.

The valve topwork 174 is shown as comprising a cylinder 178, a pistonreciprocable in said cylinder and a diaphragm 182 defining an expansiblechamber 184 between the upper end of the piston 180 and the cylinder178.

The chamber 184 is directly supplied by the pressure line 176.

The valve stem 104 is axially and integrally connected with the piston180 for reciprocation therewith.

The main air supply 84 is connected with the valve 172 via a supply line186. The valve 172 is connected to the input or main air inlet of therelay 76 via an input line 188 and the branch pressure output port 102of the said relay is connected back through the valve 172 via an outputline 190. When the relay is connected in the pneumatic circuit, the mainair line 186 is connected through the valve 172 with the relay inputline 188 and the relay output line 190 is connected with the chamber 184in the valve topwork 174 via the manual valve 172 and the line 176.

Operation Referring again to FIGURE 1, the operation of the embodimentshown therein will now be described.

[A] An assumed condition to facilitate an exemplary description ofoperation for all of the foregoing embodiments is that the outputs l and0 from the computer 16 are duration modulated as a function of thesensed variations in process parameters, such that either the relayswitch 12 or the relay switch 14 in the system input means will beenergized for various periods of time. This results in a selectivecompletion of either a first motor circuit comprising power lead P 21common terminal 18, contact 26, line 28, motor terminal 30, common motorterminal 22 and power lead P; or a second motor circuit comprising powerlead P common terminal 18, contact 32, lead 34, motor terminal 36,common motor terminal 22 and power lead P The said first circuitenergizes the [servo] motor 24 for counter-clockwise rotation for theduration of a zero state output signal from the "0 terminal of thecomputer 16 while the said second circuit energizes the [servo] motor 24for clockwise rotation for the duration of a unit state output signalfrom the 1 terminal of the computer 16.

Referring specifically to FIGURE 1, and assuming a clockwise rotation ofthe output shaft 40 of the [servo] motor 24, the manual override wheel42, hub 44 and leakport control cam 46 are all rotated in a clockwisedirection for the duration of the unit state signal from the computer16, after which the relay switch 14 will open and de-energize the[servo] motor 24.

On clockwise rotation, the control cam 46 raises the control follower 48and consequently, the leakport 64 via the combination of throttlingrange slide 68 and leakport supporting arm 66. Thus, instantaneously,the leakport 64 is moved away from the leakport lever 130 permitting agreater flow therethrough to atmosphere. This results in a decrease inthe pilot pressure in the pilot chamber 74 of the relay 76 since thesaid pilot chamber is supplied at a constant rate of flow via thepressure port 80 and in-line restrictor 82, the variable being exhaustflow via the pressure tube 72 and leakport 64.

The reduction in pressure causes the spacer assembly 94 and diaphragms96 and 98 to move upward in response to the force differential betweenthe branch and pilot chambers 86 and 74, respectively, whereby thefloating seat 90 is raised from the upper end of the relay poppet 88 andthe branch pressure begins to exhaust to atmosphere via the exhaustchamber 92 and exhaust port 100.

Thus, referring additionally to FIGURE 3, an exhaust of branch pressurein the relay 76 results in a lowering of the branch pressure at theoutput port 102 thereof, causing a corresponding outflow and reductionin pressure in the expansible chamber 184 of the valve topwork 174 viathe line 176, valve 172 and output line 190.

Assuming that the piston 180 is conventionally biased to move into thecylinder 178, such as by a compression spring SP coaxial with the valvestem 104, a reduction of pressure in the chamber 184 will result in adecreased force opposing the piston 180 and the piston 180 and valvestem 104 will move upwardly relative to the positions shown in FIGURES land 3 in response to the said decrease in branch pressure and the forceexerted thereon by the compression spring SP.

This causes the integral extension 108, see FIGURE 1, on the valve stem104 to follow the stem 104 in its upward displacement and tend toslacken the chain 110.

The torsion spring 128 has already been constrained to store energy bythe clockwise rotation of the control cam 46 and thus, via the feedbackcam, second feedback pinion, first feedback pinion and drum shaft 114 tobias the drum 112 to rotate in a counter-clockwise direction.

The feedback chain is wound on the drum 112 to be taken up thereby inthe biased direction of rotation thereof. Thus, an upward displacementof the valve stem 104 causes the chain 110 to tend to slacken and betaken up by the drum 112 which rotates through an angle directlyproportional to the said displacement. This permits the feedback cam122, via the drum shaft 114, first and second fedback pinions 118 and116 and rotary shaft 120 to follow the control cam in clockwise rotationin an amount proportional to the displacement of the valve stem 104. Theresult is to constrain the leakport lever to follow the upwarddisplacement of the leakport 64 via the feedback cam contour 124 andfeedback cam follower 134 to decrease the leakport flow and tend tobalance the entire system by creating an increase in pressure in thepilot chamber 74 of the relay 76.

The valve stem 104 will continue to be displaced until the pilotpressure decrease imposed on the system via the signal input to the[servo] motor 24 has been completely nullified by the action of thefeedback means 106' constraining the leakport lever 130 to follow theleakport 64 until the flow therethrough has been modulated to adecreased value sufficient to restore the initial value of pilotpressure in the pilot chamber 74 of the relay 76. The restoration ofinitial pilot pressure eliminates the differential between the branchand pilot chambers 86 and 74, respectively, and the floating valve seat90 is reseated on the relay poppet 88, holding the branch pressure atits resulting lower controlled value and balancing the relay. The valvestem 104 and its associated process control valve means (not shown) havenow fully responded to the constraint imposed on the system by theoutput signal from the computer 16 and have been displaced in an amounthaving a preselected functional relationship to the state and durationof the said computer output signal.

Referring now to FIGURE 2, and assuming the same clockwise rotation ofthe motor shaft 40 and the other conditions assumed for FIGURE 1, thefirst input pinion is rotated clockwise with the shaft 40 and drives theleakport positioning disk assembly 144 in a counterclockwise directionvia the second input pinion 142.

As a result, the leakport 154 is moved through the same angle ofrotation as the motor shaft 40 in a pcripheral arc determined by theposition of the control lever on the integral shelf 146 of thepositioning assembly 144.

This displacement of the leakport 154 is away from the leakport leverwhich, instantaneously, remains in a fixed position, resulting in anincreased flow through the leakport and a resulting drop in pilotpressure in the pneumatic relay 76.

As previously described with respect to FIGURES 1 and 3, and referringnow additionally to FIGURE 3, the drop in pilot pressure causes adecrease in branch pressure which is transmitted from the relay outputport 102 to the expansible chamber 184 of the process control valvetopwork 174 via pressure line 170, valve 172 and pressure line 176. Theresulting effect, as previously described, is to cause the piston andthe integral process control valve stem 104 to be displaced upward withrespect to the position shown in FIGURES 2 and 3.

Initially, because of the torsion spring coupling comprising the firstand second torsion springs 164 and 166,

respectively and the axial interconnecting spacer 168 therebetween, theleakport lever 170 is biased to follow the leakport 154. However, thestop pin 162 on the control disk assembly 160 engages the lower surfaceof and imposes a constraint on the leakport lever 170, via the feedbackmechanism 158, whereby the leakport lever 170 only follows the leakport154 at a rate and through an angular displacement, respectively,proportional to the rate of displacement and displacement of the processcontrol valve stem 104. The upward displacement of the valve stem 104permits the chain 110, via the extension 108, to tend to slacken. Thebias of the torsion springs 164 and 166 cause the control disk assembly160 to rotate counter-clockwise, whereby, via the shaft 120, the secondfeedback pinion 118 rotates counter-clockwise, the first feedback pinion116 is driven clockwise and the drum shaft 114 and drum 112 rotateclockwise with the said first feedback pinion 116 to take up the slackin the chain.

The leakport lever 170 will rotate toward the leakport 154 and the pilotpressure in the relay 76 will thus be continuously modulated toward afinal increased value which will balance the relay 76 when the valvestem 104 has reached a final position in satisfaction of the constraintimposed on the entire system by the durationmodulated input from thecomputer 16 to the [servo]- motor 24.

The continuous modulation of pilot pressure in both the embodiments ofFIGURES 1 and 2 prevents overshoot of the valve stem 104 with respect tothe desired displacement imposed thereon by the input signal. Thesystem, in both embodiments is thereby rendered highly stable.

The throttling range or operating range of the system is controlled, inthe embodiment of FIGURE 1, by longitudinally displacing the range slide68 along the bifurcated section of the control follower 48. This movesthe leakport 64 longitudinally of the leakport lever 130, whereby therelative angular displacement of the leakport 64 and leakport lever 130is selectively varied, producing a corresponding variation in the rangeof flow rates and resulting pilot pressures which can be effected.

In the embodiment of FIGURE 2, the leakport 154 is movable radially withrespect to the axis of rotation of the control disk assembly 160, viathe pivoted control lever 150, whereby the relative angular displacementbetween the leakport 154 and the leakport lever 170 to effect avariation in the throttling range as described above with respect toFIGURE 1.

In case of electric power failure or malfunction, both the embodimentsof FIGURES 1 and 2 are provided with manual override means for placinginput constraints on the system. Rotation of the manual override disk 42of FIGURE 1 or the positioner disk assembly 144 of FIGURE 2 will causethe same resulting control of the valve stem 104 as is provided by therotation of the motor shaft 40 of the [servoIl-motor 24.

This invention provides a position-balanced transducer means forselectively positioning a displaceable control means in response to anelectric control signal, said transducer means including an electricmotor means displaceable in response to said control signal, a pressureregulator means including a pressure control means, adapted to bedisplaced by said motor means, efiecting a pressure control signal inresponse to a displacement of said motor means, said pressure controlsignal being adapted to energize said displaceable control means, andposition responsive feedback means connected with and displaceable bysaid displaceable control means, superimposing a compensatingdisplacement on said pressure control means to eflect a position balancebetween the final position assumed by said displaceable control meansand the displacement effected in said electric motor means by saidelectric control signal.

[Thus] Further, as described above, this invention provides a novelcomputer-coordinated process control wherein a process parameter issensed by the computer and converted to a duration modulated binary orother multistate output signal; the computer output signal isselectively coupled, according to its state to the input terminals of abi-directional or multi-directional [servo-] motor, respectively; the[servo-] motor produces a directional output displacement proportionalto the duration of the input signal state and in a direction determinedby the said signal state and imposes a functionally related displacementon a leakport away from its associated leakport lever via suitablecontrol means; the leakport displacement causes a functionally relatedpilot pressure variation in a control relay means which produces abranch pressure output functionally related to the change in pilotpressure; the branch pressure variation causes a repositioning, via afluid or pneumatic motor means, of displaceable controller element suchas a process control valve stem; the controller element causes afunctionally related displacement to be imparted to the leakport lever,via a feedback means, whereby the leakport lever is constrained tofollow the leakport at a rate determined by the rate of displacement ofthe controller element and continuously modulate the pilot pressureuntil the change in pilot pressure has been overcome, whereby the relaywill be balanced and the controller element will be stopped after adisplacement determined by the duration modulated signal and thevariation in the process parameter sensed by the computer will becorrected.

It is to be understood that the various embodiments of the inventionshown and described herein are for the purpose of example only and isnot intended to limit the scope of the appended claims.

What is claimed is:

1. A process control means for controlling process parameters comprisinginput means for sensing a variation in a process parameter and producinga duration-modulated multiple state electric signal in response thereto,electro-pneumatic converter means for producing a pneumatic pressurechange having a predetermined functional relationship with said electricsignal, said pressure change comprising an increase or decrease ofpneumatic pressure determined, respectively, by the state of saidelectric signal, said increase or decrease having a [manitude] magnitudeproportional to the duration of said signal in a respective statethereof, displaceable controller means actuated by said pneumaticpressure from a first position through a displacement having a directiondetermined by the state of said electric signal and a magnitudedetermined by the duration of said signal in a respective state thereof,and feed back means interconnecting said controller means and saidconverter means, said feedback means acting on said converter means tocontinuously modulate said converter means in response to thedisplacement of said controller means until the elfect of said pressurechange on said controller means is equalized, whereby said controllermeans will stop in a second [potion] position.

2. The invention defined in claim 1, wherein said electro-pneumaticconverter comprises multi-directional electric [servo-] motor meanshaving motor output means actuated through a predetermined displacementand in a direction determined by the duration and state, respectively,of said duration-modulated multiple-state electric signal, a pneumaticrelay having a branch pressure chamher and a pilot chamber with aconstant source of pressure supplied thereto, a variable bleed meansconnected with said pilot chamber to variably exhaust pressure therefromand control the pilot pressure therein, first control means for saidvariable bleed means driven by said motor output means for varying thebleed rate thereof in response to said duration-modulated multiple-statesignal, whereby said pilot pressure is varied causing said relay to varythe branch pressure in said branch pressure chamber; a second controlmeans for said variable bleed means and resilient means interconnectingsaid first and second control means and biasing said second controlmeans to counteract said first control means, said displaceablecontroller means including pneumatic motor means actuated in response tosaid branch pressure and a displacealble means adapted to be displacedby said pneumatic motor means; and said feedback means comprises drivemeans interconnecting said displaceable means and said second controlmeans, said drive means acting to constrain said second control means inaccordance with the rate of displacement of said displaceable means,whereby the affect of said first control means on said variable bleedmeans is continually modulated during displacement of said displaceablemeans.

3. The invention defined in claim 2, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises lever means pivoted at oneend and carrying said leakport at the other end, and first rotary cammeans driven by said motor shaft and engaging said lever meansintermediate the ends thereof; said second control means comprises aleakport lever pivoted at one end and positioned adjacent the leakportintermediate its ends and a second rotary cam means engaging saidleakport lever intermediate its ends for constraining said leakportlever with respect to said leakport; and said feedback means comprises agear train, first and second shaft means interconnected through saidgear train, a drum axially connected to said first shaft means,elongated flexible means wound on said drum at one end thereof andconnected with said displaceable means at the other end, said secondshaft means being axially connected with said second rotary cam means.

4. The invention defined in claim 2, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises a first rotary controlassembly driven by said motor shaft and support means on said assemblyretaining said leakport on said assembly radially of the axis ofrotation thereof; said resilient means comprises a torsion means; saidsecond control means comprises a leakport lever extending radially fromthe axis of said torsion means at one end to a position adjacent saidleakport intermediate its ends and a second rotary control assemblyengaging said leakport lever intermediate its ends for constraining saidleakport lever with respect to said leakport against the action of saidtorsion means; and said feed-back means comprises a gear train, firstand second shaft means interconnected with said first shaft means,elongated flexible means wound on said drum at one end thereof andconnected with said displaceable means at the other end, said secondshaft means being axially connected with said second rotary controlassembly.

5. [In] For use in a process control system including computer means forsensing variations in process parameters and generating multiple-stateduration-modulated electric signals in response thereto and furtherincluding a displaceable controller means for controlling saidparameters, said controller being displaced by a pneumatic motor means,the invention comprising electro-pneumatic converter means for producinga branch pressure for actuating said pneumatic motor means and saidcontroller means to produce a displacement of said controller meanshaving a magnitude and direction determined by the duration and state,respectively, of said electric signals, said converter means comprisingmulti-directional electric [servo-] motor means having motor outputmeans actuated through a predetermined displacement and in a directiondetermined by the said duration and state, respectively, of saidelectric signal, a pneumatic relay having a branch pressure chamber anda pilot chamber with a constant source of pressure supplied thereto, avariable bleed means connected with said pilot chamber to variablyexhaust pressure therefrom and control the pilot pressure therein, firstcontrol means for said variable bleed means driven by said motor outputmeans for varying the bleed rate thereof in response to said electricsignal, whereby said pilot pressure is varied causing said relay to varythe branch pressure in said branch pressure chamber, a second controlmeans for said variable bleed means and resilient means interconnectingsaid first and second con trol means and biasing said second controlmeans to counteract said first control means.

6. The invention defined in claim 5, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises lever means pivoted at oneend and carrying said leakport at the other end, and first rotary cammeans driven by said motor shaft and engaging said lever meansintermediate the ends thereof; and said second control means comprises aleakport lever pivoted at one end and positioned adjacent the leakportintermediate its ends, and a second rotary cam means engaging saidleakport lever intermediate its ends for constraining said leakportlever with respect to said leakport, said second rotary cam means beingdriven in response to a displacement of said displaceable controllermeans.

7. The invention defined in claim 5, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises a first rotary controlassembly driven by said motor shaft and support means on said assemblyretaining said leakport on said assembly radially of the axis ofrotation thereof; said resilient means comprises a torsion means; andsaid second control means comprises a leakport lever extending radiallyfrom the axis of rotation of said torsion means at one end to a positionadjacent said leakport intermediate its ends and a second rotary controlassembly engaging said leakport lever intermediate its ends forconstraining said leakport lever with respect to said leakport againstthe action of said torsion means, said second rotary control assemblybeing driven in response to a displacement of said displaceablecontroller means.

[8. In a process control system including computer means for sensingvariations in process parameters and generating multiple-stateduration-modulated electric signals in response thereto and furtherincluding a displaceable controller means for controlling saidparameters, said controller being displaced by a pneumatic motor means,the invention comprising the combination of electropneumatic convertermeans for producing a branch pressure for actuating said pneumatic motormeans and said controller means to produce a displacement of saidcontroller means having a magnitude and direction determined by theduration and state, respectively, of said electric signals, and feedbackmeans interconnecting said controller means and said electric-pneumaticconverter means, said feedback means acting on said converter means tocontinuously modulate said converter means until the affect of saidpressure change on said controller means is equalized] 9. [The inventiondefined in claim 8,] For use in a process control system including meansfior sensing varia tions in process parameters and generating electriccontrol signals in response thereto and further including a displaceablecontroller means for controlling said parameters, said controller beingdisplaced by a pneumatic motor means, the invention comprising thecombination of elccrro-pneumatic converter means including displaceablepressure control means for producing a branch pressure for actuatingsaid pneumatic motor means and said controller means to produce adisplacement of said controller means in response to said electricsignals, and displacement fcedback means interconnecting said controllermeans and said electro-pneumaric converter means, said feedback meansacting on said displacewble control means of said converter means toqontinuously modulate said converter means until the afiect of saidpressure change on said controller means is equalized; wherein saidconverter means comprises [multi-directional] electric [servo] motormeans having motor output means actuated through a predetermineddisplacement [and in a direction determined by the said duration andstate, respectively, or] in response to said electric signal, apneumatic relay having a branch pressure chamber and a pilot chamberwith a constant source of pressure supplied thereto, a variable bleedmeans qomprising said displaceable pressure control means connected withsaid pilot chamber to variably exhaust pressure therefrom and controlthe pilot pressure therein, first control means for said variable bleedmeans driven by said motor output means for varying the bleed ratethereof in response to said electric signal, whereby said pilot pressureis varied causing said relay to vary the branch pressure in said branchpressure chamber, a second control means for said variable bleed meansand resilient means interconnecting said first and second control meansand biasing said second control means to counteract said first controlmeans; and said feedback means compnises drive means interconnectingsaid displaceable controller means and said second control means, saiddrive means acting to constrain said second control means in accordancewith the rate of displacement of said [displacable] displaceablecontroller means, whereby the affect of said first control means on saidvariable bleed means is continually modulated during displacement ofsaid displaceable controller means.

10. The invention defined in claim 9, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises lever means pivoted at oneend and carrying said leakport at the other end, and first rotary cammeans driven by said motor shaft and engaging said lever meansintermediate the ends thereof; said second control means comprises aleakport lever pivoted at one end and positioned adjacent the leakportintermediate its ends and a second rotary cam means engaging saidleakport lever intermediate its ends for constraining said leakportlever with respect to said leakport; and said drive means of saidfeedback means comprises a gear train, first and second shaft meansinterconnected through said gear train, a drum axially connected to saidfirst shaft means, elongated flexible means wound on said drum at oneend thereof and connected with said displaceable controller means at theother end, said second shaft means being axially connected with saidsecond rotary cam means.

11. The invention defined in claim 9, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises a first rotary controlassembly driven by said motor shaft and support means on said assemblyretaining said leakport on said assembly radially of the axis ofrotation thereof; said resilient means comprises a torsion means; saidsecond control means comprises a le'akport lever extending radially fromthe axis of said torsion means at one end to a position adjacent saidleakport intermediate its ends and a second rotary control assemblyengaging said leakport lever intermediate its ends for constraining saidleakport lever with respect to said leakport against the action of saidtorsion means; and said drive means of said feedback means comprises agear train, first and second shaft means interconnected through saidgear train, a drum axially connected with said first shaft means,elongated flexible means wound on said drum at one end thereof andconnected with said displaceable controller means at the other end, saidsecond shaft means being axially connected with said second rotarycontrol assembly.

12. Position-balanced transducer means efiecting a constrained positionoutput in response to an electric control signal input comprisingelectric motor means having an output means displaceable in response toan electric control signal applied to said electric motor means,pressure regulator means including pressure control means displaceableby said output means eflecting a pressure output signal in response to adisplacement of said ,output means, pressure operated controller meansdisplaceable in response to said pressure output signal, and feedbackmeans interconnected with said controller means and said output meansand responsive to the position of said controller means superimposing acompensating displacement on said displaceable pressure control meansthrough said output means to eflect a position balance between theposition assumed by said controller means and the displacement effectedin said electric motor means by said electric control sigrwl.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 2,789,543 4/1957 Popowsky 91-387 2,985,808 5/ 1961Ketchledge 31820.209 3,038,449 6/1962 Murphy et al 91--36 3 3,040,715 6/1962 McCombs et a1. 91-382 3,101,031 8/1963 Crossley 91-387 PAUL E.MASLOUSKY, Primary Examiner.

